IS-IS stands for Intermediate System to Intermediate System. Initially it was introduced by “Intermediate system to Intermediate system routing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473)”, ISO/IEC 10589 (1992). It was originally designed for the connectionless network, and then it was enhanced by Callon, R., “OSI IS-IS for IP and Dual Environment”, RFC 1195 (December 1990), so that IS-IS can be used on the IP network.